Today there are a wide range of intravascular prostheses on the market for use in the treatment of aneurysms, stenoses, and other vascular irregularities. Balloon expandable and self-expanding stents are well known for restoring patency in a stenosed vessel, e.g., after an angioplasty procedure, and the use of coils and stents are known techniques for treating aneurysms.
Previously-known self-expanding stents generally are retained in a contracted delivery configuration using a sheath, then self-expand when the sheath is retracted. Such stents commonly have several drawbacks, for example, the stents may experience large length changes during expansion (referred to as “foreshortening”) and may shift within the vessel prior to engaging the vessel wall, resulting in improper placement. Additionally, many self-expanding stents have relatively large delivery profiles because the configuration of their struts limits further compression of the stent. Accordingly, such stents may not be suitable for use in smaller vessels, such as cerebral vessels and coronary arteries.
Other drawbacks associated with the use of coils or stents in the treatment of aneurysms is that the devices, when deployed, may have a tendency to straighten or otherwise remodel a delicate cerebral vessel, which may cause further adverse consequences. Moreover, such devices may not adequately reduce blood flow from the cerebral vessel into the sac of the aneurysm, which may increase the likelihood of rupture. Generally, if a greater surface area is employed to cover the sac, the delivery profile of the device may be compromised due to the increased surface area, and the device also may be more rigid and cause remodeling of the vessel.
For example, PCT Publication WO 00/62711 to Rivelli describes a stent comprising a helical mesh coil having a plurality of turns and including a lattice having a multiplicity of pores. The lattice is tapered along its length. In operation, the plurality of turns are wound into a reduced diameter helical shape, then constrained within a delivery sheath. The delivery sheath is retracted to expose the distal portion of the stent and anchor the distal end of the stent. As the delivery sheath is further retracted, subsequent individual turns of the stent unwind to conform to the diameter of the vessel wall.
The stent described in the foregoing publication has several drawbacks. For example, due to friction between the turns and the sheath, the individual turns of the stent may bunch up, or overlap with one another, when the delivery sheath is retracted. U.S. Pat. Nos. 4,768,507 to Fischell et al. and 6,576,006 to Limon et al., each describe the use of a groove disposed on an outer surface of an interior portion of the stent delivery catheter, wherein at least a portion of the stent is disposed within the groove to prevent axial movement during proximal retraction of the sheath. However, the approach described in those patents results in a larger profile for the delivery catheter than might otherwise be possible.
In addition, once the sheath of the delivery catheter is fully retracted, the turns of a ribbon-type stent may shift within the vessel prior to engaging the vessel wall, resulting in improper placement of the stent. Still further, because the distal portion of the stent may provide insufficient engagement with the vessel wall during subsequent retraction of the remainder of the sheath, ambiguity concerning accuracy of the stent placement may arise.
In addition, when using a ribbon-type stent to restore patency to a vessel following angioplasty, it typically is necessary to first insert a dilatation catheter over a pre-placed guide wire, perform angioplasty, remove the balloon dilatation catheter, and then insert the stent delivery catheter. To minimize the procedure time and trauma associated with exchanging the stent delivery catheter for the balloon dilatation catheter, it would be advantageous to provide a stent delivery catheter for ribbon-type stents that in addition included a balloon component for performing angioplasty prior to delivering the stent.
In view of these drawbacks of previously known devices, it has been proposed in copending and commonly assigned U.S. patent application Ser. No. 10/342,427, filed Jan. 13, 2003, to provide an implantable vascular prosthesis comprising a ribbon-type stent body joined at its distal end to a radially expandable anchor. As described in that application, the radially expandable anchor is deployed first to anchor the distal-most portion of the ribbon-type stent body, thereby enhancing accuracy of placement of the prosthesis.
Although the prosthesis described in the above-mentioned application overcomes many of the drawbacks of previously know ribbon-type stents, it has been observed that some proximal movement of the radially expandable anchor may occur during proximal withdrawal of a sheath used to retain the anchor in its delivery configuration.
It further would be desirable to provide means for anchoring a distal end of the delivery catheter to the vessel wall, prior to deployment of the radially expandable anchor, so as to prevent inadvertent axial movement of the delivery catheter during withdrawal of the sheath of the delivery catheter.
It also would be desirable to provide a delivery catheter suitable for use with ribbon-type stents that permits angioplasty to be performed with the same catheter as used for stent delivery, thereby reducing complexity of the procedure and eliminating a need to exchange a stent delivery catheter for an angioplasty catheter.